Structural foam plastics are being developed for appliance, automotive and furniture uses providing lower cost, light-weight products having high utility. Such products are molded from compositions that will foam under molding conditions wherein the gas liberating agent will provide gases in situ, at elevated molding temperatures, that blow the molded composition reducing its density by 2 to 50%.
Such foamable moldable compositions will fill injection molds readily, however, the set-up or cooling time in the mold has been longer than for conventional molding causing molding costs to be higher, offsetting the lower material cost advantages.
It is the objective of the present invention to provide foamable polyblend compositions that can be foamed and molded simultaneously with shorter cycles than conventional foamable polymeric materials.
U.S. Pat. No. 3,268,636 discloses a process for the injection molding of foamed plastic articles, teaching the general concepts of molding foamable plastic using thermoplastics and various blowing agents.
The present invention relates to moldable foamable polyblends of relative high density that can be used as structural tough molded articles for furniture, appliances and automotive. Styrenic plastics such as styrene-acrylonitrile copolymers and rubber reinforced polymers (ABS) are used conventionally for such molded articles having high modulus and toughness along with excellent melt flow properties for molding. Such materials when foamed with aliphatic blowing agents ar plasticized with the blowing agents, hence, lose modulus and more importantly have longer set-up times or molding cycles.
It has been found, unexpectedly, that polyblends of high heat distortion interpolymers, in particular, the alkyl half esters of alkenyl aromatic-maleic anhydride interpolymers with ABS polyblends, in amounts of 1 to 10% by weight, provide polyblends that foam readily to produce fine cell structure yet provide moldable polymeric polyblend compositions that have reduced molding cycles and excellent structural engineering properties even though the density has been reduced 2 to 50%.